Light projecting method and device

ABSTRACT

A waveguide comprises a first surface and a second surface. The first surface comprises a first plurality of grating structures. The first surface other than the first plurality of grating structures comprises a first reflective layer. The second surface comprises a second reflective layer. The waveguide is configured to guide an in-coupled light beam to undergo reflections between the first reflective layer and the second reflective layer. The first plurality of grating structures are configured to disrupt the reflections to cause at least a portion of the in-coupled light beam to couple out of the waveguide and project from the first surface, the portion of the in-coupled light beam coupled out of the waveguide forming out-coupled light beams.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/573,510, filed on Sep. 17, 2019, and entitled“Light Projecting Method and Device”, which is a continuation-in-partapplication of U.S. patent application Ser. No. 16/036,776, filed onJul. 16, 2018, and entitled “Light Projecting Method and Device”. Theabove-referenced applications are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

This disclosure relates to methods and devices for projecting light.

BACKGROUND

Light projecting technologies are essential for enabling severalimportant device functionalities. For example, structured lightprojecting is deployed in 3D camera modules of mobile phones forrecognizing facial features. The projected light reflects off the facialfeatures can be captured by a detector and analyzed by algorithms to“perceive” the topology of the face. Accordingly, authentication, emojigeneration, image capture orientation, and other various functionalitiescan be designed based on inputs of the facial feature recognition.

Current light projecting technologies are disadvantaged for high cost,large size, and low integration, which pose as bottlenecks for thedevelopment of device functionalities built upon the light projection.Therefore, improvements over the existing light projecting technologiesare desirable for both the consumer market and the industry.

SUMMARY

Various embodiments of the present disclosure include light projectingstructures (e.g., waveguides), devices, and systems. According to oneaspect, a waveguide comprises a first surface and a second surface. Thefirst surface comprises a first plurality of grating structures. Thefirst surface other than the first plurality of grating structurescomprises a first reflective layer. The second surface comprises asecond reflective layer. The waveguide is configured to guide anin-coupled light beam to undergo reflections between the firstreflective layer and the second reflective layer. The first plurality ofgrating structures are configured to disrupt the reflections to cause atleast a portion of the in-coupled light beam to couple out of thewaveguide and project from the first surface, the portion of thein-coupled light beam coupled out of the waveguide forming out-coupledlight beams.

In some embodiments, the out-coupled light beams converge from the firstsurface to form an upright cone of light on top of the first pluralityof grating structures.

In some embodiments, the out-coupled light beams diverge from the firstsurface to form an inverted cone of light on top of the first pluralityof grating structures.

In some embodiments, the first surface is in an x-y plane comprising anx-direction and a y-direction perpendicular to each other; thein-coupled light beam propagates inside the waveguide substantiallyalong the x-direction of the x-y plane; the out-coupled light beamspropagate substantially along a z-direction normal to the x-y plane; thefirst plurality of grating structures are each associated with a gratingdepth and a duty cycle; and the first plurality of grating structures atdifferent x-direction positions have at least one of different gratingdepths or different grating duty cycles.

In some embodiments, the first surface is in an x-y plane comprising anx-direction and a y-direction perpendicular to each other; thein-coupled light beam propagates inside the waveguide substantiallyalong the x-direction of the x-y plane; the out-coupled light beamspropagate substantially along a z-direction normal to the x-y plane; thefirst plurality of grating structures are each associated with anorientation in the x-y plane with respect to the z-direction; and thefirst plurality of grating structures at different y-direction positionshave different orientations.

In some embodiments, the waveguide is a planar waveguide; the firstsurface and the second surface are parallel to each other and are thelargest surfaces of the planar waveguide; and the out-coupled lightbeams couple out of the waveguide from the first surface.

In some embodiments, the waveguide is a planar waveguide; the firstsurface and the second surface are parallel to each other and are thelargest surfaces of the planar waveguide; the first plurality of gratingstructures comprise volumetric gratings between the first surface andthe second surface; and the out-coupled light beams couple out of thewaveguide from the first surface.

In some embodiments, the waveguide further comprises an elongated thirdsurface. A light source couples light into the waveguide via the thirdsurface to form the in-coupled light beam; and the light from the lightsource is collimated into a line shape corresponding to the elongatedthird surface.

In some embodiments, the waveguide further comprises a fourth surface. Aremainder of the in-coupled light beam undergoing the reflectionsreaches the fourth surface; and the fourth surface comprises alight-absorbing material layer for absorbing the remainder of thein-coupled light beam.

In some embodiments, the waveguide further comprises a second pluralityof grating structures on at least one of the first surface or the secondsurface. A light source couples light into the waveguide via the secondplurality of grating structures to form the in-coupled light beam.

According to another aspect, a light projecting system comprises awaveguide comprising a first surface and a second surface, and comprisesa light source coupling light into the waveguide to form an in-coupledlight beam. The first surface comprises a first plurality of gratingstructures, the first surface other than the first plurality of gratingstructures comprises a first reflective layer, and the second surfacecomprises a second reflective layer. The waveguide is configured toguide the in-coupled light beam to undergo reflections between the firstreflective layer and the second reflective layer, and the firstplurality of grating structures are configured to disrupt thereflections to cause at least a portion of the in-coupled light beam tocouple out of the waveguide and project from the first surface, theportion of the in-coupled light beam coupled out of the waveguideforming out-coupled light beams.

These and other features of the systems, methods, and non-transitorycomputer readable media disclosed herein, as well as the methods ofoperation and functions of the related elements of structure and thecombination of parts and economies of manufacture, will become moreapparent upon consideration of the following description and theappended claims with reference to the accompanying drawings, all ofwhich form a part of this specification, wherein like reference numeralsdesignate corresponding parts in the various figures. It is to beexpressly understood, however, that the drawings are for purposes ofillustration and description only and are not intended as a definitionof the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of various embodiments of the present technology areset forth with particularity in the appended claims. A betterunderstanding of the features and advantages of the technology will beobtained by reference to the following detailed description that setsforth illustrative embodiments, in which the principles of the inventionare utilized, and the accompanying drawings of which:

FIG. 1 is a graphical illustration of a light projecting system, inaccordance with various embodiments of the present disclosure.

FIG. 2 is a side-view graphical illustration of an exemplary lightprojecting system for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 3 is a side-view graphical illustration of an exemplary lightprojecting device, in accordance with various embodiments of the presentdisclosure.

FIG. 4A-FIG. 4I are side-view graphical illustrations of in-couplingfrom a light source to a light projecting structure, in accordance withvarious embodiments of the present disclosure.

FIG. 5A-FIG. 5F are side-view graphical illustrations of out-couplingfrom a light projecting structure, in accordance with variousembodiments of the present disclosure.

FIG. 6A is a side-view graphical illustration of an exemplary lightprojecting device for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 6B is a graphical illustration of grating coupling efficiency withrespect to grating depth and duty cycle, in accordance with variousembodiments of the present disclosure.

FIG. 6C is a graphical illustration of the grating coupling efficiencywith respect to the grating duty cycle, in accordance with variousembodiments of the present disclosure.

FIG. 7A is a perspective-view graphical illustration of a lightprojecting device for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 7B is a graphical illustration of a dot array corresponding to theout-coupled light beams, in accordance with various embodiments of thepresent disclosure.

FIG. 8A is a perspective-view graphical illustration of a lightprojecting device for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 8B is a graphical illustration of the out-coupled light beam anglewith respect to the grating period, in accordance with variousembodiments of the present disclosure.

FIG. 9A is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure.

FIG. 9B is a graphical illustration of the out-coupled light beam anglewith respect to the grating rotation angle, in accordance with variousembodiments of the present disclosure.

FIG. 10 is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure.

FIG. 11 is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure.

FIG. 12 is a graphical illustration of an exemplary light projectingsystem for projecting light, in accordance with various embodiments ofthe present disclosure.

FIG. 13 is a graphical illustration of an exemplary light projectingsystem for projecting light, in accordance with various embodiments ofthe present disclosure.

FIG. 14 is a graphical illustration of an exemplary light projectingsystem for projecting light, in accordance with various embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Light projection is a key step for various applications such as 3Dfeature detection and 3D mapping. For example, depth camera modules usedfor industrial parts inspection and medical examination requiredetermining depth information. Referring to FIG. 1, in suchapplications, one or more light sources (e.g., a component of a lightprojecting system 102) may project structured light beams of apredetermined pattern onto an object (e.g., object 104 such as a face),and reflections of the light beams are captured by a detector (e.g., adetector 103) to measure various optical parameters. The lightprojecting system 102 and the detector 103 may be disposed on the samedevice (e.g., a device 101) or different devices. Though shown asseparate components, the detector 103 may be a part of the lightprojecting system 102 and configured to receive reflections of theprojected light beams off multiple locations on the distant object 104to determine distances of the multiple locations relative to the lightprojecting system 102. The light projecting system 102 may beimplemented on various systems or devices, such as mobile phones,computers, pads, wearable devices, vehicles, etc. A perfectly flatreflective plane at the position of the object may be used as areference, and reflections of the projected light off the reference canbe predetermined as reference reflection beams. The facial features canbe determined based on the differences between the detected reflectionbeams and the reference reflection beams, manifested as shifts ordistortions of the reference reflection beams. Such determination methodmay be known as the triangulation method.

Current light projection technologies for projecting the structuredlight beams employ a projection of a random dot array. The random dotarray is achieved by randomly arranging a plurality of lasers, whichinevitably drives up the cost and module size and increases integrationdifficulty.

To at least mitigate the disadvantages of the current technologies,light projecting systems and methods are disclosed. In variousembodiments, a light source may couple a light beam into a waveguide viaa surface of the waveguide, which then projects multiple beams viagratings on another surface to form distributed output beams. The lightsource can be a single laser (e.g., an edge-emitting laser, avertical-cavity surface-emitting laser (VCSEL)), a light-emitting diode,or the like, therefore obviating the need for multiple laser as requiredin existing technologies. The manufacturing cost can be further lowered,because the waveguide can be fabricated by standard lithographytechnologies. Moreover, the overall size of the light projecting systemcan be reduced due to the availability of integrating the waveguide on asubstrate.

As understood by people of ordinary skill in the art, a waveguide is astructure that guides waves (e.g., electromagnetic waves (light) as inthis disclosure) with minimal loss of energy by restricting expansion toone or more dimensions.

To that end, in some embodiments, a light projecting system comprises awaveguide comprising a first surface and a second surface, the firstsurface comprising a first plurality of grating structures, a lightsource coupling light into the waveguide to form an in-coupled lightbeam, and a detector. The first surface other than the first pluralityof grating structures comprises a first reflective layer, and the secondsurface comprises a second reflective layer. The waveguide is configuredto guide the in-coupled light beam to undergo reflections (e.g., totalinternal reflections, reflections other than total internal reflections)between the first reflective layer and the second reflective layer. Thegrating structures (e.g., each of the first plurality of gratingstructures) are configured to disrupt the reflections to cause at leasta portion of the in-coupled light beam to couple out of the waveguide,the portion of the in-coupled light beam coupled out of the waveguideforming out-coupled light beams. The detector is configured to receivereflections of the out-coupled beams off multiple locations on a distantobject to determine distances of the multiple locations relative to thelight projecting system. Thus, the topology of the object's surface canbe determined. A light projecting device comprising the light source andthe light projecting structure (e.g., waveguide) is described in moredetails below with reference to FIG. 2 and FIG. 3. The light projectingsystem may further comprise a projection lens structure also describedin FIG. 2. The out-coupled light passes through the projection lensstructure to reach the distant object.

FIG. 2 is a side-view graphical illustration of an exemplary lightprojecting system 102 for projecting light, in accordance with variousembodiments of the present disclosure. The light projecting system 102may be implemented on various systems or devices, such as mobile phones,computers, pads, wearable devices, vehicles, etc.

As shown in FIG. 2, the exemplary light projecting system 102 maycomprise a light projecting device 211 and an optional projection lensstructure 231 (or referred to as projector lens). In some embodiments,the light projecting device 211 may comprise a light source 201 and alight projecting structure 202. The light source 201 may comprise asingle laser (e.g., an edge-emitting laser, a vertical-cavitysurface-emitting laser (VCSEL)), a light-emitting diode (LED) with lightcollimation, or the like. Alternatively, the light source 201 maycomprise multiple lasers or diodes (e.g., an edge-emitting laser array,a VCSEL array, a LED array). The light projecting structure 202 maycomprise a waveguide described in more details below. The out-coupledlight from the light projecting structure 202 can be surface normal,focusing, or defocusing.

In some embodiments, light beams emerging from the light projectingdevice 211 (out-coupled beams) may couple out from a surface of thelight projecting device 211. Then, optionally, the light beams may passthrough the projection lens structure 231 to be projected into thespace. That is the projection lens structure 231 (e.g., one or morelenses) may be disposed above the waveguide (e.g., above a first surfaceof the waveguide described later). The projection lens structure 231 maybe configured to receive the out-coupled beams and project theout-coupled beams into an environment containing the distant object.Alternatively, the light beams may be directly projected from the lightprojecting device 211 into the space. The projection lens structure 231may comprise various lens or lens combinations (e.g., one to six piecesof separate lenses) for controlling directions of the projected beams.

In some embodiments, the projection lens structure 231 may be configuredto increase or decrease the field of view of the projected beam array.For example, the projection lens structure 231 may increase the field ofview by diverging the projected beam array, or decrease the field ofview by converging the projected beam array.

In some embodiments, the projection lens structure 231 may be configuredto collimate the each out-coupled beam. For example, per workingdistance requirement of different applications, the laser waist of theprojected beam array as collimated by the projection lens structure 231can vary from 10 mm to 1 meter. Thus, the projection lens structure 231may collimate the output light to form clear image (e.g., a dot array)at a distance of interest (e.g., in the range of 10 cm to 10 m dependingon the application).

FIG. 3 is a side-view graphical illustration of an exemplary lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 3 and presented below are intended to be illustrative.

In some embodiments, the light source 201 emits light to opticallycouple into the light projecting structure 202 at an in-coupling(coupling light into the light projecting structure 202) area of onesurface. The in-coupling setup can comprise end coupling, gratingcoupling, prism coupling, or the like. After entering the lightprojecting structure 202, the light undergoes reflections within thelight projecting structure 202 between a first surface and a secondsurface. The light projecting structure 202 may be made of a highrefractive index material (e.g., plexiglass, quartz glass, singlecrystal silicon, fused silica, etc.). In one embodiment, the reflectionscomprise total internal reflections. In one example, if the reflectionsare total internal reflections and quartz glass with a refractive indexof 1.45 is used, the critical angle for total internal refraction is 44degrees. The total internal reflections are sustained when the lighttraveling within the light projecting structure 202 strikes the first orsecond surface of the light projecting structure 202 at an angle largerthan the critical angle with respect to the normal to the surface. Inone embodiment, the reflections may not follow the total internalreflection condition. The light travelling in the light projectingstructure 202 may couple out of the light projecting structure 202 atvarious out-coupling areas (e.g., on the first surface). For example,the out-coupling areas may be areas having out-coupling structures(e.g., a transmissive grating, a reflective grating, a reflector, etc.).

In some embodiments, the light projecting structure 202 comprises afirst surface and a second surface. At least one of the first surface orthe second surface comprises a first plurality of grating structures. Inthis disclosure, the grating structure may refer to a grating (e.g.,optical grating), which is a regularly spaced collection of identical,parallel, and elongated elements. In this figure, for example, a profileof a ridge grating is shown, and each ridge grating may compriseidentical, parallel, and elongated ridges (see Grating A in FIG. 7A).The light projecting structure guides an in-coupled light beam toundergo reflections between the first surface and the second surface.

In one embodiment, the first surface (other than the first plurality ofgrating structures if they are on the first surface) may comprise afirst reflective layer 333 a, the second surface (other than the firstplurality of grating structures if they are on the second surface) maycomprise a second reflective layer 333 b, and the light projectingstructure guides the in-coupled light beam to undergo reflectionsbetween the first reflective layer 333 a and the second reflective layer333 b. If the reflected in-coupled light beam strikes a gratingstructure, a portion of the in-coupled light beam may couple out of thelight projecting structure 202, for example, from the first surface, andthe remaining portion may be reflected to continue the reflectionswithin the light projecting structure 202. The reflective layer may ormay not extend to any outer surface of the light projecting structure202. For example, the first reflective layer may comprise a firstcladding layer as an outer layer and the first reflective layer as aninner layer of the light projecting structure 202, and the secondreflective layer may comprise a second cladding layer as an outer layerand the second reflective layer as an inner layer of the lightprojecting structure 202. In one example, as shown, the first reflectivelayer 333 a as a part of the first surface does not extend to the topouter surface of the light projecting structure 202, as a cladding layer333 c may be laid on top of the first reflective layer 333 a, and thesecond reflective layer 333 b as a part of the second surface extends tothe bottom outer surface of the light projecting structure 202.

In some embodiments, the first and second reflective layers may eachcomprise one or more sub-layers of metal (e.g., alloy) and/or non-metal(e.g., dielectric). In one example, the first and second reflectivelayers may each comprise one or more sub-layers, each sub-layercomprising at least one of: aluminum, silver, gold, copper, titanium,chromium, nickel, germanium, indium, tin, platinum, palladium, zinc,aluminum oxide, silver oxide, gold oxide, copper oxide, titanium oxide,chromium oxide, nickel oxide, germanium oxide, indium oxide, tin oxide,platinum oxide, palladium oxide, zinc oxide, aluminum nitride, silvernitride, gold nitride, copper nitride, titanium nitride, chromiumnitride, nickel nitride, germanium nitride, indium nitride, tin nitride,platinum nitride, palladium nitride, zinc nitride, aluminum fluoride,silver fluoride, gold fluoride, copper fluoride, titanium fluoride,chromium fluoride, nickel fluoride, germanium fluoride, indium fluoride,tin fluoride, platinum fluoride, palladium fluoride, or zinc fluoride.

Each of the first plurality of grating structures disrupts thereflections to cause at least a portion of the in-coupled light beam tocouple out of the light projecting structure, the portion of thein-coupled light beam coupled out of the light projecting structurebeing an out-coupled light beam. Thus, one in-coupled beam travellinginside the waveguide may couple out the waveguide through the gratingsto obtain multiple out-coupled light beams. The various in-coupling andout-coupling mechanisms are described in more details below.

FIG. 4A-FIG. 4I are side-view graphical illustrations of in-couplingfrom a light source to a light projecting structure (e.g., a planarwaveguide), in accordance with various embodiments of the presentdisclosure. The structure and operations shown in FIG. 4A-FIG. 4I andpresented below are intended to be illustrative. Assuming, the planarwaveguide is in a horizontal position, in FIG. 4A, FIG. 4F, FIG. 4G,FIG. 4H, and FIG. 4I, the light source 201 may emit light substantiallywithin a horizontal plane, while the out-coupling light propagatessubstantially within a vertical plane. In FIG. 4B, FIG. 4C, FIG. 4D, andFIG. 4E, the light source 201 may emit light substantially within avertical plane, while the out-coupling light propagates substantiallywithin the vertical plane. The horizontal and vertical planes arerelative to each other and do not constitute limitations relative to theenvironment.

In some embodiments, as shown in FIG. 4A, light emitted from the lightsource 201 may couple into the light projecting structure 202 by “endcoupling” via a surface of the light projecting structure 202. Therefractive index of the environment of the in-coupling light, therefractive index of the light projecting structure 202, the wavelength,and the incident angle of the in-coupling light on the third surface ofthe light projecting structure 202 may comply with “end coupling”conditions as understood by people skilled in the art. Inside the lightprojecting structure 202, the light undergoes reflections between thefirst and second surfaces of the light projecting structure 202, andout-couples from the first surface of the light projecting structure202. Alternatively, if the light source 201 is large compared to thethird surface, a lens may be used to focus the light from the lightsource 201 into the light projecting structure 202 by “end coupling.”

In some embodiments, as shown in FIG. 4B and FIG. 4C, light emitted fromthe light source 201 may couple into the light projecting structure 202by “grating coupling” via an in-coupling grating. That is, the lightprojecting structure may further comprise a second plurality of gratingstructures on at least one of the first surface or the second surface. Alight source couples light into the light projecting structure via thesecond plurality of grating structures to form the in-coupled lightbeam. In FIG. 4B, the in-coupling grating may be fabricated on the firstsurface of the light projecting structure 202. Though the in-couplinggrating is shown to be level with the first surface, it may bealternatively elevated or depressed from the first surface, as long asmaintaining the subsequent reflections. The refractive index of theenvironment of the in-coupling light, the refractive index of the lightprojecting structure 202, the geometry of the in-coupling grating, thewavelength, and the incident angle of the in-coupling light on the thirdsurface of the light projecting structure 202 comply with “gratingcoupling” conditions as understood by people skilled in the art. Insidethe light projecting structure 202, the light undergoes reflectionsbetween the first and second surfaces of the light projecting structure202, and out-couples from the first surface of the light projectingstructure 202. FIG. 4C is similar to FIG. 4B except that the in-couplinggrating may be fabricated on the second surface of the light projectingstructure 202.

In some embodiments, as shown in FIG. 4D to FIG. 4I, light emitted fromthe light source 201 may couple into the light projecting structure 202by “prism coupling” via a prism. That is, the light projecting structuremay further comprise a prism disposed on at least one of: the firstsurface, the second surface, or the third surface. A light sourcecouples light into the light projecting structure via the prism to formthe in-coupled light beam. In this disclosure, “being disposed on” anobject also includes “being disposed close to” the object. Any gapbetween the prism and the light projecting structure 202 may be filledwith an optical glue or another refractive index matching material.

In FIG. 4D, the prism may be disposed on the third surface of the lightprojecting structure 202. The light source 201 may be disposed at theside the second surface and emit light into the prism. The lightundergoes one reflection within the prism and couples from the prisminto the light projecting structure 202 at the third surface. Therefractive index of the prism, the refractive index of the lightprojecting structure 202, the geometry of the prism, and the incidentangle of the light from the light source 201 comply with “gratingcoupling” conditions as understood by people skilled in the art. Insidethe light projecting structure 202, the light undergoes reflectionsbetween the first and second surfaces of the light projecting structure202, and out-couples from the first surface of the light projectingstructure 202. FIG. 4E is similar to FIG. 4D except that the prism maybe inverted, so that the light source 201 is disposed at the side thefirst surface.

In FIG. 4F, the prism may be disposed on the first surface of the lightprojecting structure 202. The light source 201 may emit light thatenters the prism. At the first surface between the prism and the lightprojecting structure 202, evanescent mode of the light may couple intothe light projecting structure 202. The refractive index of the prism,the refractive index of the light projecting structure 202, the geometryof the prism, and the incident angle of the light from the light source201 comply with “phase matching” conditions as understood by peopleskilled in the art. Inside the light projecting structure 202, the lightundergoes reflections between the first and second surfaces of the lightprojecting structure 202, and out-couples from the first surface of thelight projecting structure 202. FIG. 4G is similar to FIG. 4D exceptthat the prism may be disposed on the second surface of the lightprojecting structure 202.

In some embodiments, FIG. 4H is similar to FIG. 4D where the lightundergoes one reflection at the slope surface within the prism beforecoupling into the light projecting structure 202, except that the prismis disposed on the first surface. FIG. 4I is similar to FIG. 4H, exceptthat the prism is disposed on the second surface. The prism used in FIG.4F and FIG. 4G may be a regular prism, and the prism used in FIG. 4H andFIG. 4I may be a wedge prism.

FIG. 5A-FIG. 5F are side-view graphical illustrations of out-couplingfrom a light projecting structure (e.g., a planar waveguide), inaccordance with various embodiments of the present disclosure. Thestructure and operations shown in FIG. 5A-FIG. 5F and presented beloware intended to be illustrative. For simplicity, in-coupling and lighttraveling inside the light projecting structure 202 are omitted in FIG.5A-FIG. 5F.

In some embodiments, the light projecting structure comprises a planarwaveguide. The first surface and the second surface are parallel to eachother and are the largest surfaces of the planar waveguide. Theout-coupled light beams couple out of the light projecting structurefrom the first surface. The first surface or the second surfacecomprises the first plurality of grating structures. When the secondsurface comprises the first plurality of grating structures, the lightprojecting structure may further comprise a metal layer disposed on thesecond surface. Alternatively, the first plurality of grating structurescomprise volumetric gratings between the first surface and the secondsurface. That is, the in-coupled light inside the light projectingstructure 202 undergoes reflections. While the rest continuesreflections, a portion of the light may break free of the reflectionswhen striking an out-coupling structure on the first surface, on thesecond surface, or inside the waveguide, and subsequently exit thewaveguide from one of its surfaces (e.g., the first surface). Variousout-coupling structures (transmissive grating, reflective grating,reflector, etc.) are described below.

In FIG. 5A-FIG. 5C, the illustrated waveguide structure includinggratings may allow one or multiple diffraction orders to couple out ofthe waveguide. In some embodiments, as shown in FIG. 5A, gratings may befabricated at various out-coupling areas on the first surface of thelight projecting structure 202. The out-coupling areas may correspond toareas of reflections, and a portion of the light traveling inside thewaveguide may couple out of the waveguide from each of the out-couplingareas (e.g., into the air).

In some embodiments, as shown in FIG. 5B (configuration 1), diffractiongratings may be fabricated at various out-coupling areas on the secondsurface of the light projecting structure 202. That is, that waveguidemay comprise: (1) a bottom layer with gratings fabricated on top, thebottom layer having a first refractive index, and (2) a top layer with acomplementary shape with the bottom layer. The out-coupling areas maycorrespond to areas of reflections, and a portion of the light strikingeach of the out-coupling areas may bend toward the first surface andsubsequently couple out of the waveguide from the first surface.

Similarly, FIG. 5B also illustrates a configuration 2 with gratingsfabricated on the second surface. The gratings may have the samerefractive index as the waveguide or have a different refractive index.

In some embodiments, as shown in FIG. 5C, a micro lens array may bedisposed on the first surface corresponding to the positions of theout-coupling areas in FIG. 5B, such that the out-coupling light can becollimated, made parallel, or otherwise controlled.

In some embodiments, as shown in FIG. 5D, refractive gratings may befabricated at various out-coupling areas on the first surface of thelight projecting structure 202. For example, gratings of a triangleprofile as shown may be etched away from the first surface. The gratingscorrespond to the out-coupling areas, from which a portion of thereflection light may couple out of the waveguide.

In some embodiments, as shown in FIG. 5E, reflective gratings may befabricated at various out-coupling areas on the second surface of thelight projecting structure 202. For example, gratings of a triangleprofile as shown may be etched away from the second surface. Thegratings correspond to the out-coupling areas, from which a portion ofthe reflection light may be reflected towards the first surface andsubsequently couple out of the waveguide.

In some embodiments, as shown in FIG. 5F, volumetric gratings may befabricated within the waveguide. For example, the periodicity of thevolumetric gratings is in alternating refractive index between repeatingperiodic sections. The refractive index changing interfaces maycorrespond to the out-coupling areas, from which a portion of thereflection light may be reflected towards the first surface andsubsequently couple out of the waveguide.

Various configurations of the first plurality of grating structures maycontrol the out-coupled light beams. As described below, theout-coupling efficiency may be determined by the grating depth (alsoreferred to as “thickness”) and grating duty cycle (FIG. 6A-FIG. 6C),the angle of the out-coupled light beam with respect to surface normalmay be determined by the grating period (FIG. 8A-FIG. 8B), and therotation angle of the out-coupled light beam may be determined with thegrating orientation (FIG. 9A-FIG. 9B).

In some embodiments, the gratings (first plurality of gratingstructures) disrupt the reflections to cause the out-coupled light beamsto project from the first surface, and the out-coupled light beams areconfigured to form an array of dots on a surface where the out-coupledlight beams are projected on. For example, the out-coupled light beamsmay form an array of dots on a plane parallel to the first surface. Inone example, the out-coupled light beams propagates normal to the firstsurface, and a cross-section of the out-coupled light beams parallel tothe first surface comprises a random array of dots corresponding to theout-coupled light beams. In another example, the out-coupled light beamsdiverge from the first surface to form an inverted cone of light, and across-section of the inverted cone parallel to the first surfacecomprises a random array of dots corresponding to the out-coupled lightbeams (FIG. 7B). In another example, the out-coupled light beamsconverge from the first surface to form an upright cone of light andthen diverge to form an inverted cone of light above the upright cone oflight; and a cross-section of the upright or inverted cone parallel tothe first surface comprises the array of dots corresponding to theout-coupled light beams. As described below, the dot pattern is notlimited to the illustrated examples, and may comprise various otherconfigurations. The descriptions below with reference to FIG. 6A to FIG.9B may borrow the coordinate system shown in FIG. 10 or FIG. 11. Thatis, the first surface (or the second surface) of the waveguide is in anx-y plane comprising an x-direction and a y-direction perpendicular toeach other, the in-coupled light beam propagates inside the lightprojecting structure substantially along the x-direction of the x-yplane, and the out-coupled light beams propagate substantially along az-direction normal to the x-y plane. The grating structures may berandomly distributed in the x-y plane with respect to corresponding (x,y) positions. In some embodiments, the dimension of the grating is about2 μm to 30 μm, the number of gratings on the waveguide is about couplehundreds to one million, and the average pitch (separation betweenclosest gratings) is about 5 μm to 100 μm.

In some embodiments, the out-coupled light beams converge from the firstsurface to form an upright cone of light on top of the first pluralityof grating structures. For example, the upright cone may originate fromand cover all of the grating structures (e.g., hundreds of gratings) onthe first surface. In some embodiments, the out-coupled light beamsdiverge from the first surface to form an inverted cone of light on topof the first plurality of grating structures. For example, the invertedcone may originate from and cover all of the grating structures (e.g.,hundreds of gratings) on the first surface (e.g., an inverted cone oflight corresponding to dash lines of FIG. 7A).

FIG. 6A is a side-view graphical illustration of an exemplary lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 6A and presented below are intended to be illustrative.FIG. 6A may correspond to FIG. 5A described above, and the gratingout-coupling mechanism is described below.

In some embodiments, the direction of the out-coupled light beam mayfollow the following formula:

$\begin{matrix}{{\sin \theta_{m}} = {\frac{m\lambda}{\Gamma} - {n \times \sin \mspace{14mu} \theta_{i}}}} & (1)\end{matrix}$

where m is the diffraction order, λ is the wavelength, Γ is the periodof the grating, n is the refractive index of the waveguide, θ_(m) is theangle of the out-coupling beam with respect to the normal of the firstsurface, and θ_(i) is the angle of the beam undergoing reflectionsinside the waveguide with respect to the normal of the first surface.

In some embodiments, the described out-coupling (light undergoingreflections inside a waveguide couples out of the waveguide from areashaving grating structures) occurs when the effective index of the +1diffractive order (m=1) matches the effective index of the modesupported by the waveguide. Thus, to obtain out-coupling beamspropagating parallel to the normal, and therefore (that is, θ_(m)=0),the grating period (labeled as “period” in the figure) can be obtainedas:

$\begin{matrix}{\Gamma = \frac{\lambda}{n \times sin\theta_{i}}} & (2)\end{matrix}$

For example, when the waveguide is quartz glass (n=1.45), λ=940 nm, andθ_(i)=60°, Γ can be obtained to be 748 nm. Accordingly, the gratingperiod can affect the angle of the out-coupling beam with respect to thenormal.

Substituting equation (2) into equation (1), it can be obtained that:

sin θ_(m)=(m−1)×n×sin θ_(i)   (3)

Further, if the reflections follow total internal reflections, and basedon the condition for total internal reflection with a critical angleθ_(c):

$\begin{matrix}{{\theta_{i} > \theta_{c}} = {\arcsin \left( \frac{1}{n} \right)}} & (4)\end{matrix}$

It can be obtained that

${{\sin \; \theta_{i}} > \frac{1}{n}},$

and therefore:

n×sin θ_(i)>1   (5)

To satisfy both (3) and (5) with m being an integer and |sin θ_(m)|≤1, mcan only be 1. Therefore, the described out-coupling (light undergoingtotal internal reflection inside a waveguide coupling out of thewaveguide from areas having the grating structures) may yield only them=+1 order of out-coupled light, without interference of light of othertransmissive diffraction orders. This is one of the advantages absent inexisting light projecting technologies.

FIG. 6B is a graphical illustration of simulated coupling efficiencywith respect to grating depth and duty cycle, in accordance with variousembodiments of the present disclosure.

In some embodiments, the grating has a geometry for a high couplingefficiency, that is, the percentage (portion) of the light undergoingreflections that couples out of the waveguide at the grating. Thus, inthis context, the coupling efficiency can be understood as anout-coupling efficiency. When the grating period is fixed, the couplingefficiency is determined by the grating depth and duty cycle (percentageof each period that the ridge structure occupies). Referring to thelabels “ridge width” and “period” in FIG. 6A and FIG. 9A, the duty cyclemay be obtained as dividing the ridge width by the period. The dutycycle may be alternatively be referred to as a filling factor. For FIG.6B, when λ=940 nm, and θ_(i)=60°, Γ can be obtained to be 748 nm.

FIG. 6B shows simulated coupling efficiencies for two differentwaveguide modes (that is, TE mode and TM mode light traveling in thewaveguide). The x-axis represents the duty cycle, and the y-axisrepresents the grating depth. Higher coupling efficiencies arerepresented by brighter areas. For the TE mode, the highest couplingefficiency is 9.8%, occurring at duty cycle of 0.43 and a thickness of0.35 μm. For the TM mode, the highest coupling efficiency is 2.8%,occurring at duty cycle of 0.52 and a thickness of 0.3 μm. Therefore,the grating depth and duty cycle can be designed to achieve variouscoupling efficiencies. Further, by tuning the grating depth, a couplingefficiency higher than the illustrated 9.8% efficiency can be achieved.

In one example, extracting from the TE mode diagram in FIG. 6B, whenλ=940 nm, θ_(i)=60°, Γ=748 nm, and thickness=0.35 μm, the couplingefficiency with respect to the duty cycle can be obtained as shown inFIG. 6C. The same peak coupling efficiency is at 9.8%, with a duty cycleof 0.43 and a thickness of 0.35 μm.

In some embodiments, as a portion of the light undergoing reflections inthe waveguide couples out of the waveguide at each grating, the power ofthe light remaining in the waveguide decreases after each out-couplingevent. To ensure that out-coupled light beams in the dot array haveabout similar powers, the gratings can be designed such that thecoupling efficiency increases as the distance of the grating from thelight source 201 increases. For example, referring back to FIG. 6A,grating Y can have a larger coupling efficiency than that of grating X,by tuning the duty cycle and grating depth, to ensure that theout-coupled light from grating Y and grating X have similar powers.

Thus, in some embodiments, each of the grating structures is associatedwith an out-coupling efficiency. The out-coupling efficiency increasesmonotonically along the x-direction. The out-coupling efficiency dependson a grating depth and a duty cycle of the grating structure. At leastone of a grating depth or a duty cycle of the grating period varies inthe x-direction to cause the out-coupling efficiency to increasemonotonically along the x-direction. In one example, a grating depth ofthe grating structure increases monotonically in the x-direction,causing the out-coupling efficiency to increase monotonically along thex-direction. In another example, a duty cycle of the grating structureincreases monotonically in the x-direction causing the out-couplingefficiency to increase monotonically along the x-direction. In anotherexample, the x-y plane comprises a plurality of regions corresponding tovarious ranges of positions along the x-direction, the regionscomprising a first region and a second region. The first region is theclosest to an area of the in-coupled light beam coupling into the lightprojecting structure. The second region is the furthest from the area ofthe in-coupled light beam coupling into the light projecting structure.The grating structures in the same region have similar out-couplingefficiencies. The monotonic increase of the out-coupling efficiencyalong the x-direction causes a power of the out-coupled light beam fromeach of the grating structures in the first region to be similar to apower of the out-coupled light beam from each of the grating structuresin the second region.

FIG. 7A is a perspective-view graphical illustration of a lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 7A and presented below are intended to be illustrative.

As shown in FIG. 7A, in some embodiments, the light projecting structure202 may comprise a planar waveguide with gratings fabricated on thefirst surface. The light projecting structure 202 shown in FIG. 7A maybe similar to the light projecting structure 202 shown in FIG. 6A,except that the out-coupling light beams in FIG. 7A are normal to thefirst surface. The light source 201 may comprise one or more lasers orLEDs with light collimation. The lasers or LEDs may be arranged in a rowto couple into a side surface of the planar waveguide.

In some embodiments, the gratings (e.g., grating A, grating B, gratingC, grating D, etc.) may be fabricated at random locations on the firstsurface. The gratings may have the same grating period. From eachgrating, one out-coupling light beam couples out of the waveguide.Accordingly, when viewed from top, the out-coupling light beams may forma random dot array as shown in FIG. 7B. The illustrated dot arraypattern is merely exemplary. Based on configuring the grating structures(e.g., by tuning period, orientation, depth, duty cycle, (x, y, z)positions on the waveguide, number, etc.), any dot array pattern can beachieved to satisfy the application requirements.

FIG. 8A is a perspective-view graphical illustration of a lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 8A and presented below are intended to be illustrative.

The light projecting device 211 may be similar in FIG. 7A and FIG. 8A,also providing a random dot array, except that the gratings in FIG. 8Amay have different grating periods. As shown in FIG. 8A, in someembodiments, the gratings (e.g., grating E, grating F, grating G,grating H, etc.) may have different grating periods Γ. According toequation (1) described above, θ_(m) changes with the grating period Γ.That is, the out-coupling light beam may propagate at various angleswith respect to the normal direction. Thus, the change in θ_(m) may alsoincrease the randomness of the dot array. A plot of the out-coupledlight beam angle (in the x-z plane with respect to the z-direction)against the grating period is shown in FIG. 8B. As shown, within thesame vertical plane normal to the first surface and along the directionof the light traveling inside the waveguide (x-direction), theout-coupled light beam can be manipulated between −5 to 15 degrees withrespect to the normal direction, by changing the grating period. Thoughthe out-coupled beam may also have a y-direction component, FIG. 8A andFIG. 8B focus on the x-direction component.

Thus, in some embodiments, the grating structures are each associatedwith a period, and the period varies for the grating structures alongthe x-direction. The variation of the period causes the out-coupledlight beams to couple out of the waveguide at a range of angulardeviations in the x-direction. In one example, the period monotonicallyvaries along the x-direction. The monotonic variation of the periodalong the x-direction causes the out-coupled light beams to couple outof the light projecting structure at a range of angular deviations inthe x-direction.

FIG. 9A is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure. As shown in FIG. 9A, in some embodiments, the gratings mayhave various orientations within the x-y plane. The grating orientationcan be illustrated with reference to the orientation of the ridges ofthe grating. For example, grating M may be oriented with its ridgesperpendicular to the x-direction, grating N may be oriented with itsridges at a positive rotation angle to the x-direction, and grating Kmay be oriented with its ridges at a negative rotation angle to thex-direction.

In some embodiments, the in-coupled light travels from left to rightinside the waveguide in the x-direction. The out-coupled light fromgrating M has a y-direction component of zero. That is, ignoring thex-direction component, the out-coupled light from grating M propagatesin the z-direction. The out-coupled light from grating N of a positiverotation angle has a negative y-direction component. That is, ignoringthe x-direction component, the out-coupled light from grating Npropagates in the z-negative-y direction. The out-coupled light fromgrating K of a negative rotation angle has a positive y-directioncomponent. That is, ignoring the x-direction component, the out-coupledlight from grating K propagates in the z-positive-y direction. Thus,considering the out-coupled beams from the gratings M, N, and, K, theout-coupled beams converge in the y-z plane. FIG. 9A is a simplifiedillustration of the grating orientation control described below in FIG.10 for obtaining converging out-coupled beams. The reverse of FIG. 9Bfor obtaining diverging out-coupled beams is described below in FIG. 11.

A plot of the out-coupled light beam angle (in the y-z plane withrespect to the z-direction) against the grating rotation angle (withrespect to the x-direction) is shown in FIG. 9B. In this plot, theout-coupled light beam angle can be manipulated between about −70 to 70degrees with respect to the reference direction, by changing the gratingorientation between 45 and −45 degrees with respect to the x-direction.FIG. 9B is merely exemplary, and alternative direction reference systemsmay be used. Though the out-coupled beam may also have a x-directioncomponent, FIG. 9A and FIG. 9B focus on the y-direction component.

Thus, in some embodiments, the grating structures are each associatedwith a degree of rotation with respect to the z-direction, and thedegree of rotation varies for the grating structures along they-direction. The variation of the degree of rotation causes theout-coupled light beams to couple out of the waveguide at a range ofangular deviations in the y-direction. In one example, the degree ofrotation varies monotonically clockwise or counter-clockwise. Themonotonic variation of the degree of rotation causes the out-coupledlight beams to propagate at various y-direction components.

Each of FIG. 10 and FIG. 11 is a top-view graphical illustration ofexemplary gratings (first plurality of grating structures) on the firstsurface, in accordance with various embodiments of the presentdisclosure. Alternatively, the gratings may be fabricated on the secondsurface or according to another configuration shown in FIG. 5A-FIG. 5Fabove. The structure and operations shown in FIG. 10 and FIG. 11 andpresented below are intended to be illustrative. The gratings in FIG. 10and FIG. 11 may have combined controlling the out-coupling efficiency bythe grating depth and duty cycle, controlling the angle of theout-coupled light beam with respect to normal by the grating period, andcontrolling the rotation angle of the out-coupled light beam by thegrating orientation described above from FIG. 6A-FIG. 9B. As shown inFIG. 10 and FIG. 11, the planar waveguide is in an x-y plane, and thez-direction is the surface normal direction (which is perpendicular tothe x-y plane). In this disclosure, the x-direction and y-direction aredefined as shown in this figure. The z-direction is normal to the x-yplane and pointing out of the plane of the paper. The x, y, and zdirections may also be referred to as positive x, y, and z directions,and their opposite directions may be referred to as negative x, y, and zdirections. The in-coupled light may enter the waveguide from left,portions of which couple out of the waveguide through the gratings, withsome residue light (also referred to as remainder light) left andcontinuing in the x-direction. The in-coupled light may originate fromone or more lasers. The first grating structure is each associated witha grating depth, a duty cycle, a period, and an orientation in the x-yplane with respect to the z-direction. The first plurality of gratingstructures at different x-direction positions have at least one ofdifferent grating depths or different grating duty cycles. The firstplurality of grating structures at different x-direction positions havedifferent periods. The first plurality of grating structures atdifferent y-direction positions have different orientations.

In some embodiments, the waveguide further comprises an elongated thirdsurface opposite to the fourth surface. The position of the thirdsurface relative to the first and second surfaces are described above. Alight source couples light into the waveguide via the third surface (inthe “light incident direction” shown in FIG. 10 and FIG. 11) to form thein-coupled light beam. The light from the light source is collimatedinto a line shape corresponding to the elongated third surface. In oneexample when a single laser is used, the laser output beam may becollimated by a collimation lens or lens array into a line shape, whichlies along the third surface of the planar waveguide and cansubsequently couple into the planar waveguide through the third surface.

In some embodiments, the divergence of the out-coupled beams may becontrolled via the grating orientation and the grating period. Forexample, the divergence of the out-coupled beams in the y-direction maybe controlled via the grating orientation, and the divergence of theout-coupled beams in the x-direction may be controlled via the gratingperiod. In the y-direction of FIG. 10 and FIG. 11, the angle of theout-coupled beam in the y-z plane (a plane containing the y-directionaxis and the z-direction axis) with respect to the z-direction varieswith the rotational orientation of the grating. Detailed explanationscan be referred to the discussion above with reference to FIG. 9A andFIG. 9B. In the x-direction of FIG. 10 and FIG. 11, the angle of theout-coupled beam in the x-z plane (a plane containing the x-directionaxis and the z-direction axis) with respect to the z-direction varieswith the grating period. The output angle of the out-coupled beamincreases with the grating period. Detailed explanations can be referredto the discussion above with reference to FIG. 8A and FIG. 8B.Therefore, the grating orientation and the grating period may becontrolled to obtain converging out-coupled beams (e.g., in a cone shapeconverging from the first surface) or diverging out-coupled beams (e.g.,in an inverted cone shape diverging from the first surface).

FIG. 10 shows an exemplary grating orientation and period control forobtaining converging out-coupled beams, and FIG. 11 shows an exemplarygrating orientation and period control for obtaining divergingout-coupled beams.

In some embodiments, FIG. 10 and FIG. 11 illustrate exemplary gratingstructure with grating orientation control. In FIG. 10, the gratingorientation may change from bottom to top in the y-direction, such thatthe gratings appear to rotate clockwise with respect to the normal tothe first surface. That is, in FIG. 10, assuming that the y-axisdirection is the reference direction, the gratings in the middlehorizontal section of the first surface have no rotation, the gratingsin the bottom horizontal section of the first surface have negativerotations (tilting left), and the gratings in the top horizontal sectionof the first surface have positive rotations (tilting right), so thatthe out-coupled beam from the topmost grating has the most negativey-direction component, and the out-coupled beam from the bottommostgrating has the most positive y-direction component, consistent withFIG. 9B and its description. That is, the grating structures along they-direction may have orientations rotating in a clockwise direction tocause the out-coupled light beams to converge from the first surface ina y-z plane. In FIG. 11, the grating orientation may change from bottomto top in the y-direction, such that the gratings appear to rotatecounter-clockwise with respect to the normal to the first surface. Thatis, in FIG. 11, assuming that the y-axis direction is the referencedirection, the gratings in the middle horizontal section of the firstsurface have no rotation, the gratings in the bottom horizontal sectionof the first surface have positive rotations (tilting right), and thegratings in the top horizontal section of the first surface havenegative rotations (tilting left), so that the out-coupled beam from thetopmost grating has the most positive y-direction component, and theout-coupled beam from the bottommost grating has the most negativey-direction component, consistent with FIG. 9B and its description. Thatis, the grating structures along the y-direction have orientationsrotating in a counter-clockwise direction to cause the out-coupled lightbeams to diverge from the first surface in a y-z plane. Thus, changingthe grating orientation (e.g., clockwise or counter-clockwisemonotonically in the y-direction) expands the out-coupled light frombeing only in the surface normal direction (normal to the first surface)to having a certain field-of-view in the y-direction. The field of viewin the y-direction converges in FIG. 10 and diverges in FIG. 11,contributing to the convergence and divergence of the out-coupled beamsrespectively.

In some embodiments, FIG. 10 and FIG. 11 also illustrate exemplarygrating structure with grating period control. In FIG. 10, the gratingperiod decreases in the x-direction, so that the first out-coupled beamin the x-direction has the most positive x-direction component, and thelast out-coupled beam in the x-direction has the most negativex-direction component, consistent with FIG. 8B and its description.Thus, the out-coupled beams converge in the x-direction. In FIG. 11, thegrating period increases in the x-direction, so that the firstout-coupled beam (coupled out of the first grating) in the x-directionhas the most negative x-direction component, and the last out-coupledbeam (coupled out of the last grating) in the x-direction has the mostpositive x-direction component, consistent with FIG. 8B and itsdescription. Thus, changing the grating period (e.g., increasing ordecreasing monotonically in the x-direction) expands the out-coupledlight from being only in the surface normal direction (normal to thefirst surface) to having a certain field-of-view in the x-direction. Theperiod may decrease monotonically in the x-direction to cause theout-coupled light beams to converge from the first surface in an x-zplane. The period may increase monotonically in the x-direction to causethe out-coupled light beams to diverge from the first surface in an x-zplane. The field of view in the x-direction converges in FIG. 10 anddiverges in FIG. 11, contributing to the convergence and divergence ofthe out-coupled beams respectively.

Referring to FIG. 10, the grating period's decrease (e.g., monotonicdecrease) in the x-direction combined with the grating orientation'sclockwise rotation in the y-direction (e.g., monotonic clockwiserotation with respect to the z-direction for gratings in they-direction) may cause the out-coupled light beams to converge from thefirst surface. That is, the period decreases monotonically in thex-direction and the grating structures along the y-direction haveorientations rotating in a clockwise direction to cause the out-coupledlight beams to converge from the first surface. In one example, theconverged beams may form an upright cone projected out from the firstsurface and converging towards a point above the first surface, but oncepast the converging point, the beams will diverge to form an invertedcone of light on top of the upright cone.

Referring to FIG. 11, the grating period's increase (e.g., monotonicincrease) in the x-direction combined with the grating orientation'scounter-clockwise rotation in the y-direction (e.g., monotoniccounter-clockwise rotation with respect to the z-direction for gratingsin the y-direction) may cause the out-coupled light beams to divergefrom the first surface. That is, the period increases monotonically inthe x-direction and the grating structures along the y-direction haveorientations rotating in a counter-clockwise direction to cause theout-coupled light beams to diverge from the first surface. In oneexample, the diverged beams may form an inverted cone projected out fromthe first surface and diverging from the first surface.

In some embodiments, the light power in the waveguide decreases alongthe propagation direction (x-direction in FIG. 10 and FIG. 11), andhence the power of the reflection beams impinging on the gratings forout-coupling decreases along the propagation direction. To obtain auniform output power for the out-coupled beams, the out-couplingefficiency may increase along the propagation direction to compensatefor the loss of power. The out-coupling efficiency may increasemonotonically in the propagation direction. The out-coupling efficiencycan be varied by changing the grating depth and/or grating duty cycle(see discussion of FIG. 6B and FIG. 6C above). Any out-couplingefficiency level can be achieved with an appropriate combination ofgrating depth and grating duty cycle pair. The grating thickness may ormay not increase monotonically in the propagation direction. The gratingduty cycle may or may not increase monotonically in the propagationdirection. Each of the grating thickness and the grating duty cycle doesnot have to obey any monotonic trend in the propagation direction, aslong as the combinations of the grating thickness and the grating dutyresult in increasing out-coupling efficiencies for the out-coupled beamsalong the propagation direction.

Referring to FIG. 10 and FIG. 11, in some embodiments, the first surfacecan be visualized as strips of reflection regions (Region 1, Region 2,etc.), with corresponding out-coupling efficiencies η₁, η₂, . . . ,η_(n) increasing from η₁ to η_(n) in order to maintain a constant outputpower. In one example, the relationship may beP_(n−1)×η_(n−1)=P_(n)×η_(n), where P_(n)=P_(n−1)×(1−η_(n−1)). To changethe coupling efficiency η, one can change the duty cycle and/or thegrating depth.

In some embodiments, the distribution of the grating locations on thefirst surface in FIG. 10 and FIG. 11 may be random. That is,notwithstanding complying with the described trend in grating period,grating depth, grating duty cycle, and grating orientation, if the firstsurface (or the second surface) is in an x-y plane, the gratings arerandomly distributed in the x-y plane with respect to corresponding (x,y) positions. Here, the random distribution means that the gratings maynot be fixed at periodic locations (e.g., 2D lattice locations, evenlyspaced locations, etc.) on the first or the second surface. The randomdot array described herein may correspond to this random distribution ofthe grating locations. The random distribution of the grating locationscan minimize the algorithm error that is detrimental to detection basedon the out-coupled beams. The algorithm error is often caused byperiodic or other non-random pattern trends, for which the algorithm runby the detector for detecting differences between reflections fromdifferent structured light beams would have a hard time to distinguishone part of the patterns from another part as they appear to be thesame.

Although the gratings in FIG. 10 and FIG. 11 are shown as three ridges,each grating can contain any number of ridges or another alternativegrating structure (e.g., rib, buried ridge, diffused ridge, etc.). Theridge profile may be square, round, triangular, etc. Though shown assquare in FIG. 10 and FIG. 11, the outer shape of each grating mayalternatively be circular, oval, rectangular, etc. The size of gratingmay vary from 1 period (around 1 μm) to the whole pixel size (around 30μm). In some embodiments, if the grating is sufficiently large such thatthe diffraction limit can be ignored, the dot size will increase withthe grating size, and the size of the grating can be manipulated toobtain the ideal size for the dot (beam size of projected light beam).For example, if an application requires more dots, the size of thegrating can be reduced to pack more dots into a fixed area (e.g., thefirst surface). If an application requires brighter dots (highersignal-to-noise ratio), the size of the grating can be increased sincelarger dots have more power and thus are brighter.

FIG. 12 is a graphical illustration of an exemplary light projectingsystem 102 for projecting light, in accordance with various embodimentsof the present disclosure. The light projecting system 102 may implementthe in-coupling mechanism described above with reference to FIG. 4H andthe out-coupling mechanism described above with reference to FIG. 5B(configuration 2).

In some embodiments, the waveguide further comprises a reflective layerdisposed on the second surface and covering the grating structures. Thereflective layer may comprise one or more sub-layers of metal (e.g.,alloy) and/or non-metal (e.g., dielectric). In one example, thereflective layer comprises one or more sub-layers, each sub-layercomprising at least one of: aluminum, silver, gold, copper, titanium,chromium, nickel, germanium, indium, tin, platinum, palladium, zinc,aluminum oxide, silver oxide, gold oxide, copper oxide, titanium oxide,chromium oxide, nickel oxide, germanium oxide, indium oxide, tin oxide,platinum oxide, palladium oxide, zinc oxide, aluminum nitride, silvernitride, gold nitride, copper nitride, titanium nitride, chromiumnitride, nickel nitride, germanium nitride, indium nitride, tin nitride,platinum nitride, palladium nitride, zinc nitride, aluminum fluoride,silver fluoride, gold fluoride, copper fluoride, titanium fluoride,chromium fluoride, nickel fluoride, germanium fluoride, indium fluoride,tin fluoride, platinum fluoride, palladium fluoride, or zinc fluoride.When the grating are fabricated on the second surface (as shown) or onthe first surface, some amount of optical power may leak out of thewaveguide (e.g., downward) due to symmetric first order diffraction. Tominimize or suppress such leakage and maximize the coupling efficiency,a reflective layer (e.g., metal layer or a high reflection coatinglayer) may be deposited on the second surface. The metal can bealuminum, silver, gold, copper, or another high reflection metal.

FIG. 13 is a graphical illustration of an exemplary light projectingsystem 102 for projecting light, in accordance with various embodimentsof the present disclosure. The light projecting system 102 may implementthe in-coupling mechanism described above with reference to FIG. 4H andthe out-coupling mechanism described above with reference to FIG. 3.

In some embodiments, light-absorbing material layers as shown can beused to minimize the background noise caused by leakage light fromhigher grating modes or by residue light from incomplete coupling. Tominimize emitting the residue light from the waveguide, alight-absorbing material layer may be disposed on the sidewall of thewaveguide directly (at the end of the light propagation in thewaveguide). To reduce the leakage light from other grating modes, alight-absorbing material layer may be disposed with a gap from thesecond surface, to prevent from breaking the reflection condition. Thelight-absorbing material layer can be a (colored) anodized aluminumlayer, a rough surface, a black carbon paint layer, or anotherlight-absorbing material layer.

That is, the light projecting structure may further comprise a fourthsurface, a first light-absorbing material layer, and a secondlight-absorbing material layer. A remainder of the in-coupled light beamundergoing the reflections reaches the fourth surface after theout-coupling at each of the grating structures. The fourth surfacecomprises the light-absorbing material layer for absorbing the remainderof the in-coupled light beam. The second light-absorbing material layeris parallel to the second surface and is separated by a gap from thesecond surface. The second light-absorbing material layer may absorblight that leaks out of the waveguide from the second surface. The gapmay prevent absorbing in-coupled light still travelling inside thewaveguide.

FIG. 14 is a graphical illustration of an exemplary light projectingsystem 102 for projecting light, in accordance with various embodimentsof the present disclosure. The light projecting system 102 may implementthe in-coupling mechanism described above with reference to FIG. 4H andthe out-coupling mechanism described above with reference to FIG. 3.

In some embodiments, as shown, a residue light out-coupling setup may beadded to couple the residue light out of the waveguide (at the end ofthe light propagation in the waveguide), for example, via end coupling,grating coupling, or prism coupling described above. A detector such asa monitoring photo diode (e.g., silicon, germanium, or another diode)may be used to detect the out-coupled residue light. In one example, ifany accident (e.g., chip cracking, water damage, vapor damage, laserdislocation, in-coupling prism dislocation, or another failure event)happens, the reflection condition will be broken at the failing spot (anexample of which is shown and labeled in the figure), which will resultin change of the residue light. With a thresholding algorithm, the eventof residue light changing can be timely detected by the monitoring photodiode, and the input laser can be shut off accordingly to ensure eyesafety. If the input laser is not shut off, some of the laser beams mayescape from the light projecting system with an uncontrolled power thatmay cause eye damage.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and sub-combinations are intended to fall withinthe scope of this disclosure. In addition, certain method or processblocks may be omitted in some implementations. The methods and processesdescribed herein are also not limited to any particular sequence, andthe blocks or states relating thereto can be performed in othersequences that are appropriate. For example, described blocks or statesmay be performed in an order other than that specifically disclosed, ormultiple blocks or states may be combined in a single block or state.The exemplary blocks or states may be performed in serial, in parallel,or in some other manner. Blocks or states may be added to or removedfrom the disclosed exemplary embodiments. The exemplary systems andcomponents described herein may be configured differently thandescribed. For example, elements may be added to, removed from, orrearranged compared to the disclosed exemplary embodiments.

Throughout this specification, plural instances may implementcomponents, operations, or structures described as a single instance.Although individual operations of one or more methods are illustratedand described as separate operations, one or more of the individualoperations may be performed concurrently, and nothing requires that theoperations be performed in the order illustrated. Structures andfunctionality presented as separate components in exemplaryconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements fall within the scope of thesubject matter herein.

Although an overview of the subject matter has been described withreference to specific exemplary embodiments, various modifications andchanges may be made to these embodiments without departing from thebroader scope of embodiments of the present disclosure. Such embodimentsof the subject matter may be referred to herein, individually orcollectively, by the term “invention” merely for convenience and withoutintending to voluntarily limit the scope of this application to anysingle disclosure or concept if more than one is, in fact, disclosed.

The embodiments illustrated herein are described in sufficient detail toenable those skilled in the art to practice the teachings disclosed.Other embodiments may be used and derived therefrom, such thatstructural and logical substitutions and changes may be made withoutdeparting from the scope of this disclosure. The Detailed Description,therefore, is not to be taken in a limiting sense, and the scope ofvarious embodiments is defined only by the appended claims, along withthe full range of equivalents to which such claims are entitled.

As used herein, the term “or” may be construed in either an inclusive orexclusive sense. Moreover, plural instances may be provided forresources, operations, or structures described herein as a singleinstance. Additionally, boundaries between various resources,operations, engines, and data stores are somewhat arbitrary, andparticular operations are illustrated in a context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within a scope of various embodiments of thepresent disclosure. In general, structures and functionality presentedas separate resources in the exemplary configurations may be implementedas a combined structure or resource. Similarly, structures andfunctionality presented as a single resource may be implemented asseparate resources. These and other variations, modifications,additions, and improvements fall within a scope of embodiments of thepresent disclosure as represented by the appended claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements and/or steps areincluded or are to be performed in any particular embodiment.

1. A waveguide, comprising: at least one surface, wherein: the at leastone surface comprises a set of grating structures; the waveguide isconfigured to guide an in-coupled light beam from the light source totravel along the waveguide; and the set of grating structures areconfigured to cause at least a portion of the in-coupled light beam tocouple out of the waveguide from the at least one surface, the portionof the in-coupled light beam coupled out of the waveguide formingout-coupled light beams, wherein at least two grating structures in theset of grating structures couple out light in different directions. 2.The waveguide of claim 1, wherein: the out-coupled light beams convergeto form an upright cone of light above the set of grating structures. 3.The waveguide of claim 1, wherein: the out-coupled light beams divergeto form an inverted cone of light above the set of grating structures.4. The waveguide of claim 1, wherein: the at least one surface is in anx-y plane comprising an x-direction and a y-direction perpendicular toeach other; the in-coupled light beam propagates inside the waveguidesubstantially along the x-direction of the x-y plane; the out-coupledlight beams propagate substantially along a z-direction normal to thex-y plane; the set of grating structures are each associated with agrating depth and a duty cycle; and the set of grating structures atdifferent x-direction positions have at least one of different gratingdepths or different grating duty cycles.
 5. The waveguide of claim 1,wherein: the at least one surface is in an x-y plane comprising anx-direction and a y-direction perpendicular to each other; thein-coupled light beam propagates inside the waveguide substantiallyalong the x-direction of the x-y plane; the out-coupled light beamspropagate substantially along a z-direction normal to the x-y plane; theset of grating structures are each associated with an orientation in thex-y plane with respect to the z-direction; and the set of gratingstructures at different y-direction positions have differentorientations.
 6. The waveguide of claim 1, wherein: the waveguide is aplanar waveguide; the at least one surface comprises a first surface anda second surface; the first surface and the second surface are parallelto each other and are the largest surfaces of the planar waveguide; andthe out-coupled light beams couple out of the waveguide from the firstsurface.
 7. The waveguide of claim 6, wherein: the at least one surfacefurther comprises an elongated third surface; the light source coupleslight into the waveguide via the third surface to form the in-coupledlight beam; and the light from the light source is collimated into aline shape corresponding to the elongated third surface.
 8. Thewaveguide of claim 6, further comprising a fourth surface, wherein: aremainder of the in-coupled light beam undergoing reflection reaches thefourth surface; and the fourth surface comprises a light-absorbingmaterial layer for absorbing the remainder of the in-coupled light beam.9. The waveguide of claim 6, further comprising a second set of gratingstructures on at least one of the first surface or the second surface,wherein: the light source couples light into the waveguide via thesecond set of grating structures to form the in-coupled light beam. 10.The waveguide of claim 1, wherein: the waveguide is a planar waveguide;the at least one surface comprises a first surface and a second surface;the first surface and the second surface are parallel to each other andare the largest surfaces of the planar waveguide; the set of gratingstructures comprise volumetric gratings between the first surface andthe second surface; and the out-coupled light beams couple out of thewaveguide from the first surface.
 11. A light projecting system,comprising: a waveguide comprising at least one surface, wherein the atleast one surface comprises a set of grating structures; and a lightsource coupling light into the waveguide to form an in-coupled lightbeam, wherein: the waveguide is configured to guide an in-coupled lightbeam from the light source to travel along the waveguide; the set ofgrating structures are configured to cause at least a portion of thein-coupled light beam to couple out of the waveguide from the at leastone surface, the portion of the in-coupled light beam coupled out of thewaveguide forming out-coupled light beams; and at least two gratingstructures in the set of grating structures couple out light indifferent directions.
 12. The light projecting system of claim 11,wherein: the out-coupled light beams converge to form an upright cone oflight above the set of grating structures.
 13. The light projectingsystem of claim 11, wherein: the out-coupled light beams diverge to forman inverted cone of light above the set of grating structures.
 14. Thelight projecting system of claim 11, wherein: the at least one surfaceis in an x-y plane comprising an x-direction and a y-directionperpendicular to each other; the in-coupled light beam propagates insidethe waveguide substantially along the x-direction of the x-y plane; theout-coupled light beams propagate substantially along a z-directionnormal to the x-y plane; the set of grating structures are eachassociated with a grating depth and a duty cycle; and the set of gratingstructures at different x-direction positions have at least one ofdifferent grating depths or different grating duty cycles.
 15. The lightprojecting system of claim 11, wherein: the at least one surface is inan x-y plane comprising an x-direction and a y-direction perpendicularto each other; the in-coupled light beam propagates inside the waveguidesubstantially along the x-direction of the x-y plane; the out-coupledlight beams propagate substantially along a z-direction normal to thex-y plane; the set of grating structures are each associated with anorientation in the x-y plane with respect to the z-direction; and theset of grating structures at different y-direction positions havedifferent orientations.
 16. The light projecting system of claim 11,wherein: the waveguide is a planar waveguide; the at least one surfacecomprises a first surface and a second surface; the first surface andthe second surface are parallel to each other and are the largestsurfaces of the planar waveguide; and the out-coupled light beams coupleout of the waveguide from the first surface.
 17. The light projectingsystem of claim 16, wherein: the waveguide further comprises anelongated third surface; the light source couples the light into thewaveguide via the third surface to form the in-coupled light beam; andthe light from the light source is collimated into a line shapecorresponding to the elongated third surface.
 18. The light projectingsystem of claim 16, wherein: the waveguide further comprises a fourthsurface; a remainder of the in-coupled light beam undergoing reflectionreaches the fourth surface; and the fourth surface comprises alight-absorbing material layer for absorbing the remainder of thein-coupled light beam.
 19. The light projecting system of claim 16,wherein: the waveguide further comprises a second set of gratingstructures on at least one of the first surface or the second surface;and the light source couples the light into the waveguide via the secondset of grating structures to form the in-coupled light beam.
 20. Thelight projecting system of claim 11, wherein: the waveguide is a planarwaveguide; the at least one surface comprises a first surface and asecond surface; the first surface and the second surface are parallel toeach other and are the largest surfaces of the planar waveguide; the setof grating structures comprise volumetric gratings between the firstsurface and the second surface; and the out-coupled light beams coupleout of the waveguide from the first surface.